European patent application EP-A1-0129741 describes a device comprising a flexible lamina secured in a seat of a support and carrying elements of a strain gauge transducer. The lamina has a free end cooperating with a feeler rigidly coupled to a bushing movable within a guide body fixed to the seat. The seat is sealingly closed by a rigid cover, a sealing ring arranged between the cover and the support and a resilient seal--having an opening for the feeler passage--coupled to the cover, the feeler and the guide body.
The known device can be manufactured with rather small overall dimensions, but the somewhat high number of constituent elements prevents the reduction of the overall dimensions, involves complex and long assembling operations and negatively affects the accuracy and repeatability of the measurements, that also suffer from the presence of a sliding contact between the feeler and the lamina.
Japanese patent application published under No. 52-35662 discloses a strain gauge device for checking the deformation of vessels subjected to high pressures. The device comprises a substantially C-shaped element, apparently obtained from a single piece, with a section of reduced thickness, so as to be resiliently deformable, whereto there are fixed strain gauges. The device is not provided with a real frame or support, even if there is a ring adapted to cooperate with the arms of the element for keeping them at a determined distance.
During the measurement, the ring is removed and the ends of the integral element, that act as feelers, contact relevant points of the vessel to be checked.
This device with two feelers is provided for very particular applications, for which manual operations by a rather skilled operator are necessary. Anyway, the accuracy and repeatability are inevitably poor, due to the manner in which the device cooperates with the vessel.
German patent application DE-A-3003370 shows in FIG. 2 a device for checking linear dimensions of parts comprising a support body that defines a seat and a measuring cell fixed within the seat. The measuring cell comprises an integral element having a support portion adapted to be coupled to the support body, a movable end portion carrying a feeler and an intermediate flexible portion connecting the support portion with the movable end portion. The intermediate flexible portion, that has substantially the shape of, and operates as a flat leaf spring, carries transducer means constituted by strain gauges. A member defining a protection cover terminates at one end with a coupling portion having a hole for a screw also passing through a hole of the support portion of the integral element, for locking the integral element to the support body.
German patent application DE-A-3207837 shows in FIG. 1 an electronic plug gauge for checking diameters of holes having an arm-set featuring a substantially U-shaped integral member arranged within a substantially cylindrical protection body. The integral member has two flexible portions next to the base of the member and two legs or arms, each of which is movable about a rotation axis defined by the corresponding flexible portion. Fixed at the ends of the movable arms are feelers for contacting a diametrically opposite point of the hole. A position transducer comprises two elements respectively fixed to intermediate portions of the movable arms.